While the thermogenic properties of brown adipose tissue (BAT) are well known, we recently discovered previously unknown cardioprotective properties of BAT. Mice deficient in the uncoupling protein 1 (UCP1), a protein synthetized by BAT and required for BAT thermogenic function, developed increased cardiomyocyte (CM) injury in a model of catecholamine-induced cardiomyopathy. Cardiomyocyte injury was decreased by transplantation of BAT from WT mice into UCP1-deficient (UCP1-/-) mice, suggesting that functional BAT protects against catecholamine-induced cardiac injury. In Preliminary Studies, we demonstrated that UCP1-/- mice (with dysfunctional BAT) developed greater myocardial infarction (MI) size than WT mice and had a lower level of left ventricular (LV) phosphorylated endothelial nitric oxide synthase (S1177P-NOS3) after ischemia- reperfusion (I/R) injury. We identified bone morphogenetic protein 3b (BMP-3b) as an adipokine secreted by BAT that may mediate BAT-related cardioprotection. BMP-3b increased S1177P-NOS3, decreased apoptosis in serum-deprived rat neonatal CMs and decreased MI size after I/R in WT mice in vivo. The objective of the proposed research is to investigate the cardioprotective effects of BAT and BMP-3b in cardiac I/R injury. To further investigate the cardioprotective role of BAT in I/R injury, we will determine whether UCP1- deficiency induces greater adverse LV remodeling after I/R injury, independent of MI size. We will determine whether restoring functional BAT in UCP1-/- mice and increasing functional BAT in WT mice limit MI size. In these studies, we will transplant BAT from WT mice into UCP1-/- and WT mice prior to myocardial injury. Using CM- specific NOS3-/- mice, we will explore the role of the NOS3 pathway in the cardioprotective effect of BAT. By studying BMP-3b-/- mice, we will elucidate the role of BMP-3b in I/R injury and whether BMP-3b is the adipokine in BAT that is required to limit I/R injury by studying BMP-3b-/- mice. Finally, we will investigate the mechanisms underlying the cardioprotective effects of BMP-3b and explore the potential role of BMP-3b as a treatment for I/R induced CM injury. We will assess the role of the NOS3 pathway in the cardioprotective effect of BMP-3B using both isolated mouse adult CMs and the in vivo I/R model in WT, BMP-3b-/- and CM-specific NOS3-/- mice. As a first step toward applying the results to humans, we will investigate whether BMP-3b is secreted by human brown adipocytes. We will test the effects of varying BMP-3b dose, and time of delivery relative to onset of injury, on the extent of myocardial damage in the in vivo murine I/R model. Successful completion of these aims will define and elucidate a novel cardioprotective effect of BAT in myocardial I/R injury and will characterize a previously unknown cardioprotective adipokine secreted by BAT, BMP-3b. The proposal is a first step toward identifying new cardioprotective therapies that may decrease myocardial I/R.